Blast piston circuit breaker

ABSTRACT

The circuit breaker is provided with a stationary contact, made hollow for the removal of switching gases, and a movable contact pin which is movable with the blast cylinder relative to the stationary piston. The length of the contact pin is such that the contact pin separates from the contact only when the free volume of the blast cylinder is reduced to one-half. The end of the blast cylinder slides on a tube surrounding the contact which tube has a bent end face spaced in opposition to a metal part enclosed by the stationary piston to define a planar spark gap, the diameter of which is twice as large as that of the movable contact pin.

United States Patent [1 1 Richter et al.

BLAST-PISTON CIRCUIT BREAKER Inventors: Frederich Richter; Heinz-Helmut Schramm, both of Berlin, all of Germany Assignee: Siemens Aktiengesellschaft, Munich,

Germany Filed: Apr. 10, 1972 Appl. No.: 242,380

Foreign Application Priority Data Apr. 30, 1971 Germany P 21 22 183.0

[ June 12, 1973 3,588,407 6/1971 Frink .1 200/148 A 3,659,065 4/1972 Roidt et al. 200/148 A Primary Examiner-Robert S. Macon Attorney-Hugh A. Chapin [57] ABSTRACT The circuit breaker is provided with a stationary contact, made hollow for the removal of switching gases, and a movable contact pin which is movable with the blast cylinder relative to the stationary piston. The length of the contact pin is such that the contact pin separates from the contact only when the free volume of the blast cylinder is reduced to one-half. The end of the blast cylinder slides on a tube surrounding the contact which tube has a bent end face spaced in opposition to a metal part enclosed by the stationary piston to define a planar spark gap, the diameter of which is twice as large as that of the movable contact pin.

4 Claims, 1 Drawing Figure BLAST-PISTON CIRCUIT BREAKER FIELD OF THE INVENTION This invention relates to a blast-piston circuit breaker, particularly, for high voltages. More particularly, this invention relates to a switching device for a high-voltage blast-piston circuit breaker.

BACKGROUND OF THE INVENTION Blast-piston circuit breakers have been known, for example, as in German published Pat. application No. 1,913,973, in which two hollow stationary electrodes, designed as nozzles have been connected in a closed position by a movable contact pin. The contact pin has been coupled to a blast piston which together with a cylindrical outside surface of one of the nozzle contacts defines a compressible space. The outside diameter of the nozzle electrode has been made as large as possible, in order to obtain favorable dielectric conditions. This, however, has the result that the are forming at the outer edge of the electrodes must travel relatively far to arrive at the interior of the nozzle electrode, where the most intensive exposure to the blast occurs.

Another blast-piston circuit breaker has been known, for example, in German published Pat. application No. 1,113,969, in which a cylindrical, hollow, stationary contact with a relatively small diameter has been associated with a movable, hollow contact pin, the inside diameter of which has been equal to the outside diameter of the stationary contact. The opening are which forms between the contact and the contact pin, therefore, needs to travel only a short distance until arriving at the interior of the contact and the contact pin, where the strongest blast exposure occurs. As the outside of the blast cylinder in this circuit breaker consists of metal and cooperates, for the purpose of increasing the current-carrying capacity, with an additional contact arrangement resting on the cylinder from the outside, a dielectrically favorable uniform field distribution with large area electrodes results in the open position. However, commutation of the current from the parallel contacts to the contact element and the contact pin has been possible only with a fairly large commutation voltage. Therefore, a considerable lead between the parallel contacts and the contact pin has been required in order to ensure that no arc is formed at the parallel contacts, where the arc could no longer be quenched. Further, as half of the stroke of the contact pin has been used for the precompression of the quenching medium, a rather long total stroke results.

Accordingly, it is an object of the invention to provide a blast-piston circuit breaker which improves, or at least maintains, the quenching properties thereof while reducing the space required by the circuit breaker.

It is another object of the invention to provide a blast-piston circuit breaker which can be effectively used for very high voltages.

It is another object of the invention to form a blastpiston circuit breaker with a dielectrically favorable configuration.

SUMMARY OF THE INVENTION Briefly, the blast-piston circuit breaker has a stationary contact which is hollow for the purpose of removing switching gases and which is surrounded, in known manner, by a tube having a bent over end disposed perpendicularly to the axis of the contact pin. In addition, a movable contact pin which is movable together with a blast cylinder is slidably disposed to slide between the stationary contact and tube. The blast cylinder slides over a stationary piston and includes a bent over end which slides over the tube surrounding the stationary contact to form an enclosed space.

The movable contact pin is made so long that separa tion of the movable contact pin from the stationary contact occurs only when the free volume of the blast cylinder is reduced to one-half. Further, the edge of the tube about the stationary contact and a metal part enclosed by the stationary piston are arranged opposite each other as the electrodes of a planar spark gap, the diameter of which is twice as large or larger than that of the movable contact pin. The tube with the rim on the one side, and the metal part enclosed by the piston, on the other side, thus provide an electrode surface of large area and high dielectric strength. The contact pin, on the other hand, can be dimensioned independently, according to the requirements of current conduction and are quenching. Under the action of the gas, the arc can therefore travel easily into the interior of the hollow contact where provision is made for a particularly intensive exposure to the blast by a streamlined construction. Furthermore, the relatively large diameter of the tube provides a large blast volume, as the blast cylinder rests on the outside surface of the tube via the inward-bent end face.

In order to improve the current carrying capacity of the circuit breaker, the bent over edge of the tube covers over contact fingers which surround the stationary contact and rest on the outside on the movable contact pin which surrounds the stationary contact in the closed position. The radial distance between the stationary contact and the contact pin is preferably smaller than that between the contact pin and the edge of the tube. The arc has then no reason to originate at the edge of the tube and commutates quickly to the stationary contact. The metal part opposite the tube edge can be of annular body of U-shaped cross section which faces the contact pin. The open side of this annular body can be filled with insulating material which can be used in some cases, to contribute to the quenching of the arc by giving off gas. In general, however, the arc should be extinguished before being able to act on the insulating material.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

DESCRIPTION OF THE DRAWING The drawing illustrates a cross-sectional view of a very-high voltage power circuit breaker according to the invention with the upper half shown in a closed position and the lower half shown in an open position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, only the switching device of the high-voltage circuit breaker, for example, for kilovolts (kV), is shown and the outer enclosure which is, for instance, formed by a grounded metal tank, is omitted for simplicity.

The circuit breaker includes a contact carrier 1 consisting of aluminum which leads to a terminal (not shown) and mounts a metal tube 2 thereon by means of screws 3 which pass through a flange 4 of the tube 2. A metallic intermediate body 5 is screwed into the end of the tube 2 and has a central threaded hole 6 in which a further metal tube 7 is screwed as a stationary contact. The hollow stationary contact 7 is equipped at the free end with a streamlined insert 8 of burn-off resistant material, for instance, a compact tungsten material. In addition, the contact 7 is surrounded by a tube 9 which is screwed onto the intermediate body 5 and which is provided at the free end with an inward-bent rim 10. A covered hollow space is thereby formed which accommodates contact fingers 11 which are spring loaded by suitable springs as shown.

A movable contact pin 12 which is equipped at the tip with a burn-off resistant insert 13 engages over the stationary contact 7 in the closed position of the circuit breaker. In this closed position, the contact pin 12 connects the stationary contact 7 with a sliding contact 14 which is formed by contact segments 15. The segments 15 are pressed by suitable springs 16 and 17 against the contact pin 12 on the one hand, and on the other hand against a stationary ring 20 which is fastened to a contact carrier 21. The contact carrier 21 leads to a second terminal (not shown).-

The contact pin 12 is connected via rods 22 and a star-shaped guide member 23 with a blast cylinder 25 which consists of insulating material and has a free end face 26 which is essentially conically tapered so that an edge 27 rests on the tube 2 in the closed position. When the breaker is opened, the blast cylinder 25 is pulled over a stationary piston 30, which consists of insulating material while the edge 27 slides over the tubes 2, 5 and 9, which are of the same diameter.

The piston 30 is bolted via bolts, as shown, to a metal flange 32 which is disposed at the free end of the contact carrier 21. The metal flange 32 is in metallic connection with the sliding contact 14 via the ring 20 as shown. A metal ring 34 of essentially U-shaped cross section is secured to the sliding contact 14 and is disposed within the piston 30. The hollow space of the ring 34 is lined with a plastic material 35. As will be seen, the side 36 of the metal ring 34 which faces the stationary contact 7 constitutes a planar electrode which has a large diameter as compared to the distance to the stationary contact 7. The associated counterelectrode is also a planar electrode, as such is formed by the rim 10 of the tube 9. The outer diameters of the rim l0 and side 36 are each twice as large as the diameter of the contact pin 12.

In use, the circuit breaker operates with sulfur hexafluoride as a quenching medium. The current breaker is of simple construction such that movement of the blast cylinder 25 together with the contact pin 12 suffices to generate the flow of the quenching medium. As the contact pin 12 is in engagement with the stationary contact 7 over a relatively long distance and depth of penetration into the tube 5, provision is thus made for the volume of quenching gas in the blast cylinder 25 to be reduced to onehalf before the tip 13 of the contact pin 12 is disengaged from the stationary contact 7. For this reason, a sharp blast on the breaking arc is obtained as soon as the compressed gas is discharged through the bore in the contact pin 12, on the one hand, and through the bore in the stationary contact 7 upon movement of the contact pin 12 away from the stationary contact 7. Upon breaking of the connection between the pin 12 and contact 7, the stream of quenching gas flows in the gap between the planar electrodes 10, 36 radially inwardly and drives the arc toward the burn-off insert 8. Thus, the arc reaches the region of the most intensive exposure to the blast in a short time. After the arc is extinguished, a high dielectric strength exists at the switching device as the planar electrodes 10, 36 cause in a uniform field distribution, with which the smaller spacing shown achieves a dielectric strength of 30 to 50 kilovolts per centimeter (kV/cm) in an sulfur hexafluoride (SP atmosphere at an overpressure of, for instance, 2 atmospheres.

What is claimed is:

1. A blast-piston circuit breaker having a hollow stationary contact;

a contact pin of predetermined outer diameter movably mounted with respect to said stationary contact between a first position in engagement with said stationary contact and a second position axially spaced from said stationary contact;

a tube surrounding said stationary contact and having an edge bent perpendicularly to the longitudinal axis of said stationary contact to form a planar electrode having an outer diameter at least twice as large as said diameter of said contact pin;

a stationary piston slidably receiving said contact pin therein;

a blast cylinder slidably mounted over said piston and having an inwardly bent end slidably disposed on said tube for movement with said contact pin; and

a metal part disposed within said piston in spaced facing relation to said edge of said tube to form a planar electrode and to define a planar spark gap therebetween, said metal part having an outer diameter at least twice as large as said diameter of said contact pin.

2. A blast-piston circuit breaker as set forth in claim 1 wherein said blast cylinder, said piston, said tube and said contact pin define a chamber for a predetermined volume of quenching gas and wherein said contact pin engages said stationary contact in said first piston for a length sufficient to cause said volume to decrease by one-half at the separation of said contact pin from said stationary contact during movement of said contact pin towards said second position.

3. A blast-piston circuit breaker as set forth in claim 2 wherein said contact pin is hollow and surrounds said stationary contact in said first position and which further includes a plurality of contact fingers about said stationary contact and within said tube; said contact fingers resting on said contact pin in said first position.

4. A blast-piston circuit breaker as set forth in claim 3 wherein the radial distance between said stationary contact and said contact pin is smaller than the radial distance between said contact pin and said edge of said 

1. A blast-piston circuit breaker having a hollow stationary contact; a contact pin of predetermined outer diameter movably mounted with respect to said stationary contact between a first position in engagement with said stationary contact and a second position axially spaced from said stationary contact; a tube surrounding said stationary contact and having an edge bent perpendicularly to the longitudinal axis of said stationary contact to form a planar electrode having an outer diameter at least twice as large as said diameter of said contact pin; a stationary piston slidably receiving said contact pin therein; a blast cylinder slidably mounted over said piston and having an inwardly bent end slidably disposed on said tube for movement with said contact pin; and a metal part disposed within said piston in spaced facing relation to said edge of said tube to form a planar electrode and to define a planar spark gap therebetween, said metal part having an outer diameter at least twice as large as said diameter of said contact pin.
 2. A blast-piston circuit breaker as set forth in claim 1 wherein said blast cylinder, said piston, said tube and said contact pin define a chamber for a predetermined volume of quenching gas and wherein said contact pin engages said stationary contact in said first piston for a length sufficient to cause said volume to decrease by one-half at the separation of said contact pin from said stationary contact during movement of said contact pin towards said second position.
 3. A blast-piston circuit breaker as set forth in claim 2 wherein said contact pin is hollow and surrounds said stationary contact in said first position and which further includes a plurality of contact fingers about said stationary contact and within said tube; said contact fingers resting on said contact pin in said first position.
 4. A blast-piston circuit breaker as set forth in claim 3 wherein the radial distance between said stationary contact and said contact pin is smaller than the radial distance between said contact pin and said edge of said tube. 